Magneto-optical recording medium and method of reading the same

ABSTRACT

By defining the composition of the second magnetic layer, the magneto-optical recording medium is capable of reading out at MSR whether the readout magnetic field is applied in the erasing direction or its reverse recording direction, and when a readout magnetic field is applied in the recording direction, the reading method of the magneto-optical recording medium is further enhanced in resolution.

This is a continuation of application Ser. No. 08/815,056, filed Mar.11, 1997 now patented U.S. Pat. No. 5,754,500.

BACKGROUND OF THE INVENTION

The present invention relates to a magneto-optical recording medium,such as magneto-optical disk, magneto-optical tape, and magneto-opticalcard, and a method of reading the same, and more particularly to amagneto-optical recording medium that can be reproduced at magneticallyinduced super-resolution.

In recent years, magneto-optical disks have been attracting muchattention as external storage media for computers. The magneto-opticaldisk uses an external magnetic field and a laser beam to form recordmarks of submicron size on the medium, and can achieve a drasticincrease in storage capacity as compared with other external recordingmedia such as flexible disks and hard disks.

To enable the recording of a tremendous amount of data such as movingpictures, a further increase in the storage capacity of magneto-opticaldisks is demanded. To increase the recording density, it is needed toform more record marks on the medium, that is, to define the length ofrecord mark shorter than the spot diameter of Laser beam and to narrowthe interval of record marks. Forming of such fine record marks isrelatively easy, but, there is a limit in the length of record marksthat can be read due to restrictions of the wavelength (λ) of the laserbeam to be emitted and the numerical aperture (NA) of the objectivelens.

Accordingly, various magnetically induced super-resolution (MSR) readoutmethods for reading record marks smaller than the laser beam diameterhave been proposed (Japanese Patent Application Laid-Open Nos. 1-143041(1989), 3-93056 (1991), 3-93058 (1991), 4-271039 (1992), and 5-12731(1993)). In all these conventional methods, a magneto-optical disklaminating plural magnetic layers including a recording layer and areadout layer is rotated, a readout laser beam is emitted to cause atemperature distribution in the peripheral direction of themagneto-optical disk, and record marks smaller than the spot diameterare read by making use of this temperature distribution. That is, in acertain temperature region within a spot of readout laser beam, thereadout layer has a direction of magnetization so as to mask the recordmark, and in other region, on the other hand, the direction ofmagnetization of the recording layer is transferred on the readout layerand is read out.

In these conventional methods, the record mark can be read out from aregion smaller than the spot diameter of the readout laser beam, whichsubstantially brings about the same resolution as when reading out by alight spot smaller than the spot diameter of the readout laser beam.These conventional methods, however, had the following problems. First,in the method of reading out record marks from the low-temperatureregion in the spot, although the resolution is excellent in theperipheral direction, the crosstalk by adjacent tracks is significant,or in the method of reading out record marks from the high-temperatureregion in the spot, although the crosstalk is decreased, a largeinitializing magnet is needed for initializing the readout layer, andthe apparatus is not reduced in size, and further in the method ofreading out record marks from a region changed in the direction ofmagnetization of the readout layer from the in-plane direction toperpendicular direction due to temperature distribution, although it ispossible to read out without using a large initializing magnet, thetransferred region in the spot is wide, and high readout output is notobtained.

Accordingly, the present applicant proposed an MSR readout methodcapable of solving these problems (Japanese Patent Application Laid-OpenNo. 7-244877 (1995)). FIG. 1 is a diagram showing the film compositionof the conventional magneto-optical disk capable of reading out at MSRproposed by the present applicant and the direction of magnetization inreadout. FIG. 2 is a diagram showing the state of magnetization whenerasing this magneto-optical disk, and FIG. 3 is a diagram showing thestate of magnetization when recording.

As shown in FIG. 1, a magneto-optical disk 20 is formed by laminating abase layer (not shown) made of SiN, a readout layer 21, an intermediatelayer 22, a recording layer 23 respectively made of rare-earthtransition-metal amorphous alloy, and a protective layer (not shown)made of SiN sequentially on a polycarbonate resin substrate (not shown).The readout layer 21 is transition-metal magnetization dominant, and hasan easy axis of magnetization in the perpendicular direction, that is,the lamination direction. The intermediate layer 22 is rare-earthmagnetization dominant, and has an easy axis of magnetization in thein-plane direction at room temperature (10 to 35° C.), and over apredetermined temperature higher than room temperature, the easy axis ofmagnetization is changed from the in-plane direction to theperpendicular direction. The recording layer 23 is transition-metalmagnetization dominant, and has an easy axis of magnetization in theperpendicular direction. Supposing the Curie temperatures of the readoutlayer 21, intermediate layer 22 and recording layer 23 to berespectively Tc1, Tc2 and Tc3, the relation of Tc2<Tc1, Tc2<Tc1) issatisfied. Supposing the coercive forces of the readout layer 21 andrecording layer 23 at room temperature to be respectively Hc1 and Hc3,the relation of Hc3>Hc1 is satisfied.

When erasing record marks on the magnet-optical disk 20, as shown inFIG. 2, while applying an downward erasing magnetic field, a erasinglaser beam is emitted. At this time, the region irradiated with thelaser beam is heated at curie temperature Tc3 or more, so that thedirection of magnetization of the recording layer 23 is aligned in thesame downward direction as the erasing magnetic field. A region awayfrom the erasing laser beam is cooled to room temperature. At roomtemperature, the intermediate layer 22 is an in-plane magnetized film asmentioned above, and the readout layer 21 and the intermediate layer 22are not coupled magnetically. Therefore, the direction of magnetizationof the readout layer 21 is aligned in the same downward direction as theerasing magnetic field. In the magneto-optical disk 20, meanwhile, theerasing direction is expressed downward, the recording direction, upwardreverse to the erasing direction.

When recording record marks on the magneto-optical disk 20, as shown inFIG. 3, while applying an upward recording magnetic field, a recordinglaser beam is emitted. This recording method is realized by two manners,the light modulation recording and magnetic field modulation recording.The light modulation recording is a method of irradiating by modulatingso that the intensity of laser beam may correspond to the informationwhile always applying an upward recording magnetic field, and only theregion irradiated with laser beam of high intensity has the same upwarddirection of magnetization as the recording magnetic field, so thatrecord marks are formed therein. On the other hand, the magnetic fieldmodulation recording is a method of applying by modulating the directionof magnetic field up and down so as to correspond to the informationwhile always emitting recording laser beam, and the direction ofmagnetization in the region irradiated with the laser beam is aligned inthe direction of the applied magnetic field. In making use of magneticfield modulation recording, when recording information from erasedstate, the direction of magnetization is inverted upward in the regionapplied with a magnetic field reverse to the erasing magnetic field, andrecord marks are formed therein.

A region away from the recording laser beam is cooled to roomtemperature. At room temperature, the intermediate layer 22 is anin-plane magnetized film as mentioned above, and the readout layer 21and recording layer 23 are not coupled magnetically. Therefore, thedirection of magnetization of the readout layer 21 is aligned in thedirection of magnetization by applying a small magnetic field, and it isnot necessary to use a large initializing magnet.

The state of magnetization in readout of thus recorded magneto-opticaldisk 20 is explained by reference to FIG. 1. A readout laser beam isemitted to the magneto-optical disk 20, and a downward readout magneticfield is applied to the irradiated region. In a low-temperature regionahead of the laser beam (a region lower than substantially 100° C.), theexchange coupled force between the intermediate layer 22 and recordinglayer 23 is weak, and the magnetization of the intermediate layer 22 isaligned in the direction of readout magnetic field, that is, in thedownward direction. By the exchange coupled force between theintermediate layer 22 and readout layer 21, the direction ofmagnetization of the readout layer 21 is aligned in the upwarddirection, and acts to mask the direction of magnetization of therecording layer 23 (front mask). A high-temperature region (a regionhigher than substantially 180° C.) is a region beyond the Curietemperature of the intermediate region 22, and the exchange coupledforce between the intermediate layer 22 and readout layer 21 is cut off.As a result, the direction of magnetization of the readout layer 21 isaligned in the direction of readout magnetic field, and acts to mask thedirection of magnetization of the recording layer 23 (rear mask). In anintermediate-temperature region between the low-temperature region andthe high-temperature region (a region of substantially 100° C. tosubstantially 180° C.), the direction of magnetization of the recordinglayer 23 is transferred onto the readout layer 21 by the exchangecoupled force between the recording layer 23 and readout layer 21through the intermediate layer 22.

Therefore, when a magneto-optical output is detected, since the mask isformed in the region of low temperature and region of high temperaturein the laser spot S, the magneto-optical signal is not read out from theregions, so that the magneto-optical signal is read out only from theintermediate-temperature region.

Thus, according to the magneto-optical disk proposed by the presentapplicant, the MSR readout is enabled without using large initializingmagnet, and a partial area of high-temperature region (anintermediate-temperature region) is an aperture, and a high readoutoutput is obtained, and moreover since the adjacent tracks arelower-temperature regions than the intermediate-temperature region, sothat the signal is not read out from the adjacent tracks, and thereforethe crosstalk is low.

However, when varying the direction of magnetic field applied at thetime of readout of thus constituted magneto-optical disk 20, that is,when the same upward readout magnetic field as the recording directionis applied in this magneto-optical disk 20, forming of front mask tendsto be difficult. This is because the control of exchange coupled forceis difficult at low temperature between the intermediate layer 22 andrecording layer 23 in the prior art. When a readout magnetic field inthe recording direction is applied, the direction of magnetization ofthe intermediate region 22 is not aligned with the readout magneticfield in low-temperature region, and forming of front mask is henceimperfect, and the readout characteristic deteriorates.

BRIEF SUMMARY OF THE INVENTION

The invention is devised to solve the above problems, and it is hence anobject of the invention to present a magneto-optical recording mediumcapable of reading out at MSR by applying a readout magnetic field ineither the erasing direction or its reverse recording direction, bylimiting the composition of a second magnetic layer.

To achieve the object, the invention provides a magneto-opticalrecording medium comprising a first magnetic layer formed from GdFeCo,laminated on a substrate and having characteristic of easy magnetizationin the lamination direction; a second magnetic layer formed from GdFeCo,being rare-earth magnetization dominant, laminated on the first magneticlayer and having characteristic of easy magnetization in an in-planedirection at room temperature, the second magnetic layer having acomposition of Gd_(x) (Fe_(100-y) Co_(y))_(100-x), of which x and ysatisfy respectively 26≦x≦38, 0≦y≦17; and a third magnetic layer formedfrom TbFeCo, laminated on the second magnetic layer and havingcharacteristic of easy magnetization in the lamination direction.

By irradiating the magneto-optical recording medium with a light beamaccompanied by the relative move when reading out, a temperaturedistribution is formed in the beam spot. In the low-temperature regionand the high-temperature region of this temperature distribution, thedirection of magnetization of the first magnetic layer masks thedirection of magnetization of the third magnetic layer. In theintermediate-temperature region between these regions, the direction ofmagnetization of the third magnetic layer is transferred to the firstmagnetic layer, and an aperture is formed, so that record marks smallerthan the spot diameter can be red out. In order to form a mask of thefirst magnetic layer in the low-temperature region and thehigh-temperature region, a readout magnetic field is applied in thelight beam illuminated region.

In this invention, since the second magnetic layer has the compositionsatisfying 26≦x≦38, 0≦y≦17 in Gd_(x) (Fe_(100-y) Co_(y))_(100-x), theMSR readout is enabled whether the readout magnetic field is applied inthe erasing direction for erasing all of record marks or in therecording direction reverse to the erasing direction. The relation of26≦x≦38, 0≦y≦17 is determined from the composition range of the secondmagnetic layer in which the readout characteristics such as CNR andcrosstalk may be favorable as shown in FIG. 9 to FIG. 12 below. The sizeof the aperture is smaller in the width direction of the record trackwhen the readout magnetic field is applied in the recording directionthan when applied in the erasing direction. Accordingly, when thereadout magnetic field in the recording direction is applied, a higherresolution is obtained, and the crosstalk is decreased.

In the magneto-optical recording medium of the invention, the secondmagnetic layer has a film thickness of 15 nm or more.

The film thickness of the second magnetic layer is closely related withthe strength of the exchange coupled force between the second magneticlayer and third magnetic layer, and if too thin, the exchange coupledforce is strong, and the direction of magnetization of the secondmagnetic field is not oriented in the direction of the readout magneticfield in the low-temperature region, so that mask forming may beimperfect. The practical level of readout magnetic field is 500 Oe orless, and in order to form the mask perfectly at this level, the filmthickness of the second magnetic layer is preferred to be 15 nm or more.From the viewpoint of practical thickness level of the magneto-opticalrecording medium, the maximum film thickness of the second magneticlayer is about 60 nm.

It is another object of the invention to present a reading methodfurther enhanced in resolution and decreased in crosstalk by reading outat MSR by applying a reading magnetic field in the recording direction.

To achieve the object, the invention provides a reading method of amagneto-optical recording medium, which comprises a first magnetic layerformed from GdFeCo, laminated on a substrate and having characteristicof easy magnetization in the lamination direction; a second magneticlayer formed from GdFeCo, being rare-earth magnetization dominant,laminated on the first magnetic layer and having characteristic of easymagnetization in an in-plane direction at room temperature, the secondmagnetic layer having a composition of Gd_(x) (Fe_(100-y)Co_(y))_(100-x), of which x and y satisfy respectively 26≦x≦38, 0≦y≦17;and a third magnetic layer formed from TbFeCo, laminated on the secondmagnetic layer and having characteristic of easy magnetization in thelamination direction, and records information by forming a regioninverted in the direction of magnetization from a first direction to asecond direction and a region maintaining the first direction ofmagnetization in the third magnetic layer, the method comprising thestep of irradiating a magneto-optical recording medium with a light beamaccompanied by the relative move, and the step of reading outinformation by applying a magnetic field in the second direction atleast in the region irradiated with the light beam.

Therefore, the magneto-optical recording medium is recorded by the lightmodulation recording system, that is, by emitting the recording lightbeam so that the direction of magnetization of the region heated overthe Curie temperature of the third magnetic layer is aligned in therecording direction which is the second direction. When reading out theinformation in this magneto-optical recording medium, by applying areadout magnetic field in the recording direction, the information canbe read out from the narrow aperture, and hence a high resolution isobtained and the crosstalk is decreased.

Moreover, the invention further provides a reading method of amagneto-optical recording medium, which comprises a first magnetic layerformed from GdFeCo, laminated on a substrate and having characteristicof easy magnetization in the lamination direction; a second magneticlayer formed from GdFeCo, being rare-earth magnetization dominant,laminated on the first magnetic layer and having characteristic of easymagnetization in an in-plane direction at room temperature, the secondmagnetic layer having a composition of Gd_(x) (Fe_(100-y)Co_(y))_(100-x), of which x and y satisfy respectively 26≦x≦38, 0≦y≦17;and a third magnetic layer formed from TbFeCo, laminated on the secondmagnetic layer and having characteristic of easy magnetization in thelamination direction, and records information by aligning previously thedirection of magnetization of the third magnetic layer in a firstdirection, and applying by modulating the direction of magnetic field,thereby forming a region inverted in the direction of magnetization fromthe first direction to a second direction and a region maintaining thefirst direction in the third magnetic layer, the method comprising thestep of irradiating a magneto-optical recording medium with a light beamaccompanied by the relative move, and the step of reading outinformation by applying a magnetic field in the second direction atleast in the region illuminated with the light beam.

Therefore, the magneto-optical recording medium has the direction ofmagnetization of the third magnetic layer aligned in the erasingdirection by applying the magnetic field in the erasing direction whichis the first direction previously, and is recorded by the magnetic fieldmodulation recording system, that is, by applying the recording magneticfield by modulating the direction so that the direction of magnetizationof the region heated over the Curie temperature of the third magneticlayer is aligned in the direction of the recording magnetic field. Whenreading out the information in this magneto-optical recording medium, byapplying a readout magnetic field in the second direction which isreverse to the erasing direction, the information can be read out fromthe narrow aperture, and hence a high resolution is obtained and thecrosstalk is decreased.

The above and further objects and features of the invention will morefully be apparent from the following detailed description with theaccompanying drawings.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

FIG. 1 is a diagram showing the film composition of a conventionalmagneto-optical disk and state of magnetization at the time of readout;

FIG. 2 is a diagram showing the state of magnetization at the time oferasing of the conventional magneto-optical disk;

FIG. 3 is a diagram showing the state of magnetization at the time ofrecording of the conventional magneto-optical disk;

FIG. 4 is a diagram showing the state of magnetization at the time ofreadout of a magneto-optical disk of the invention;

FIG. 5 is a film composition diagram of the magneto-optical disk of theinvention;

FIG. 6 is a graph showing the relation between the readoutcharacteristic and the power of the readout laser beam of themagneto-optical disk of the invention;

FIG. 7 is a graph showing the relation between the readoutcharacteristic and the power of the recording laser beam of themagneto-optical disk of the invention;

FIG. 8 is a graph showing the relation between the readoutcharacteristic and the readout magnetic field of the magneto-opticaldisk of the invention;

FIG. 9 is a graph showing the relation between the readoutcharacteristic and the direction of readout magnetic field with respectto x of the intermediate layer of the magneto-optical disk (lightmodulation recording) of the invention;

FIG. 10 is a graph showing the relation between the readoutcharacteristic and the direction of readout magnetic field with respectto y of the intermediate layer of the magneto-optical disk (lightmodulation recording) of the invention;

FIG. 11 is a graph showing the relation between the readoutcharacteristic and the direction of readout magnetic field with respectto x of the intermediate layer of the magneto-optical disk (magneticfield modulation recording) of the invention;

FIG. 12 is a graph showing the relation between the readoutcharacteristic and the direction of readout magnetic field with respectto y of the intermediate layer of the magneto-optical disk (magneticfield modulation recording) of the invention; and

FIG. 13 is a graph showing the dependence of readout magnetic field onthe film thickness of the intermediate layer of the magneto-optical diskof the invention.

DETAILED DESCRIPTION OF THE INVENTION

Referring now to the drawings, embodiments of the invention aredescribed in detail below.

Embodiment 1

FIG. 4 is a diagram showing the state of magnetization at the time ofreadout of a magneto-optical disk of the invention, and FIG. 5 is a filmcomposition diagram of the same magneto-optical disk. As shown in FIG.5, a magneto-optical disk 10 is formed by laminating a base layer 11made of SiN, a readout layer 13 (first magnetic layer) made of GdFeCo,an intermediate layer 14 (second magnetic layer) made of GdFeCo, arecording layer 15 (third magnetic layer) made of TbFeCo, and aprotective layer 16 made of SiN, sequentially on a polycarbonate resinsubstrate 11. The substrate 11 is 1.2 mm in thickness, and the landwidth and groove width are formed at pitches of 0.7 μm individuallytherein, so that land/groove recording is enabled. The concretecomposition and magnetic characteristic of the readout layer 13,intermediate layer 14, and recording layer 15 for constituting themagneto-optical disk 10 of the embodiment are shown in TABLE 1.

TABLE 1

The magneto-optical disk 10 having such constitution is manufactured inthe following procedure. First, in a chamber of a sputtering apparatus,targets of SiN, GdFeCo and TbFeCo are set. The substrate 11 is put intothe chamber, and the chamber internal pressure is controlled at 1×10⁻⁵Pa. Then, argon gas and nitrogen are introduced into the chamber, andeach partial pressure is adjusted to gas pressure of 0.4 Pa at 3:2(Ar:N₂). In this condition, the base layer 12 is formed on the substrate11 in a film thickness of 70 nm by DC sputtering method.

The chamber is set again to 1×10⁻⁵ Pa, and argon gas is introduced intothe chamber to 0.8 Pa, and the readout layer 13 is formed on the baselayer 12 in a film thickness of 40 nm, and sequentially the intermediatelayer 14 is formed in a film thickness of 40 nm, and the recording layer15 in a film thickness of 40 nm. Then setting the chamber once more to1×10⁻⁵ Pa, argon gas and nitrogen are fed into the chamber, and eachpartial pressure is adjusted to the gas pressure of 0.4 Pa at 3:2(Ar:N₂), and the protective film 16 is formed in a film thickness of 70nm by DC sputtering method.

In the recording layer 15 of thus manufactured magneto-optical disk 10,information is recorded magneto-optically, and the state ofmagnetization when reading it out is described below. The recordingprinciple in the magneto-optical disk 10 is same as shown in FIG. 3, andthe description is omitted herein. In this embodiment, meanwhile, therecording direction is expressed upward, the erasing direction,downward.

The magneto-optical disk 10 is irradiated with a readout laser beam, anda readout magnetic field is applied in the irradiated region in therecording direction, that is, in the upward direction. In thelow-temperature region (a region lower than about 100° C.) ahead of thelaser beam, the exchange coupled force between the intermediate layer 14and recording layer 15 is weak, and the magnetization of theintermediate layer 14 is aligned in the direction of readout magneticfield, that is, in the upward direction. Consequently, by the exchangecoupled force of the intermediate layer 14 and readout layer 13, thedirection of magnetization of the readout layer 13 is aligned downward,which functions to mask the direction of magnetization of the recordinglayer 15 (front mask). The high-temperature region (a region higher thansubstantially 180° C.) is a region above the Curie temperature of theintermediate layer 14, where the exchange coupled force between theintermediate layer 14 and readout layer 13 is cut off. As a result, thedirection of magnetization of the readout layer 13 is aligned upward inthe direction of magnetization of the readout magnetic field, whichfunctions to mask the direction of magnetization of the recording layer14 (rear mask). In the intermediate-temperature region (a region ofsubstantially 100° C. to 180° C.) between the low-temperature region andthe high-temperature region, by the exchange coupled force of therecording layer 15 and readout layer 13 through the intermediate layer14, the direction of magnetization of the recording layer 15 istransferred on the readout layer 13, thereby forming an aperture.

Thus, double masks of front mask and rear mask are formed, and when amagneto-optical output is detected, regions high and low in temperaturein the laser spot S function as the mask, and magneto-optical signal isnot read out in these regions, and the magneto-optical signal is readout only from the intermediate-temperature region.

Shown below are results of investigation of the recording and readoutcharacteristics of the magneto-optical disk 10 for MSR readout. Thewavelength λ of the semiconductor laser beam of the measuring instrumentused in readout is 685 nm, and the numerical aperture NA of theobjective lens is 0.55. The peripheral speed of the magneto-optical disk10 is 5 m/s.

With the erasing laser beam power of 8 mW, an erasing magnetic field of300 Oe was applied downward to the magneto-optical disk 10, and the fullsurface was erased. With the recording laser beam power of 8.4 mW andrecording frequency of 7.51 MHz, light modulation recording wasconducted at duty 50% while applying an upward recording magnetic fieldof 300 Oe. As a result, record marks of 0.333 μm were formed on theland. At various power levels, a reading laser beam was applied to themagneto-optical disk 10, and each CNR was measured, and the readoutpower capable of reading out with double masks was determined. Theresult is shown in the graph in FIG. 6. The ordinate indicates the CNR,and the abscissa denotes the readout power. It is known from FIG. 6 thatthe double mask MSR readout is possible by irradiation of laser beamwith readout power of 2.4 mW or more.

Similarly, varying the power of the recording laser beam, themagneto-optical disk 10 was irradiated to record information, andreadout laser beam of 3 mW was emitted to measure the CNR of themagneto-optical disk 10 of each recording power, and the dependence ofthe maximum readout signal quality on the recording power was studied.The result is shown in the graph in FIG. 7, in which the ordinaterepresents the CNR and the abscissa denotes the recording power. FromFIG. 7, a maximum CNR of 47.4 dB was obtained by irradiation of laserbeam with recording power of 6.5 mW.

Next, the dependence on readout magnetic field and crosstalk of themagneto-optical disk 10 were studied. By applying the upward (recordingdirection) readout magnetic field and downward readout magnetic field indifferent magnitude and without applying readout magnetic field, the CNRand crosstalk were measured. In the measuring method of crosstalk,record marks of five adjacent tracks are erased previously, and recordmarks are formed in the middle land, and the carrier level is measured.In the grooves at both sides of the recorded land, the carrier level issimilarly measured, and the average is determined. The differencebetween the carrier level of the land and the average carrier level ofthe groove is the crosstalk.

FIG. 8 is a graph showing this result, in which the ordinate denotes theCNR and crosstalk, and the abscissa represents the readout magneticfield, the positive direction showing the recording direction and thenegative direction showing the erasing direction. As clear from FIG. 8,when the readout magnetic field is upward, a similar CNR to the level inthe conventional downward direction was obtained, and the crosstalk waslower by about 20 dB in the embodiment of upward readout magnetic fieldas compared with the prior art. This is because the shape of theaperture is different depending on the direction of the applied readoutmagnetic field, and the application of the readout magnetic field in therecording direction is narrower in shape in the track width directionthan in the reverse direction, so that, it is expected, a lowercrosstalk is obtained.

Embodiment 2

In embodiment 2, magneto-optical disks 10 were fabricated by varying thecomposition of the magnetic layer used in the intermediate layer 14. Inthese magneto-optical disks 10, light modulation recording was effectedat recording frequency of 7.51 MHz and duty of 50%, and the readout CNRand crosstalk were studied. Supposing the composition of theintermediate layer 14 to be Gd_(x) (Fe_(100-y) Co_(y))_(100-x), themagneto-optical disks 10 were prepared in the compositions at differentvalues of x in the condition of y=6, and at different values of y in thecondition of x=31. The composition and manufacturing procedure of thereadout layer 13 and recording layer 15 and the other conditions thanthe composition of the intermediate layer 14 are same as in embodiment1, and descriptions are omitted.

First, in the magneto-optical disks 10 at various values of x in thecondition of y=6 of Gd_(x) (Fe_(100-y) Co_(y))_(100-x) of theintermediate layer 14, a readout magnetic field of 400 Oe was appliedupward (in the recording direction) and downward (in the prior art),respectively. FIG. 9 is a graph showing the results of measurement ofmaximum CNR and crosstalk at this time, in which the ordinate indicatesthe CNR and crosstalk, and the abscissa shows x%. As clear from FIG. 9,the CNR is slightly higher in the upward readout magnetic field than inthe downward direction. The crosstalk is also lower in the upwarddirection. For a practical magneto-optical disk, the CNR is required tobe 46 dB or more and the crosstalk -23 dB or less. Hence, when x is in arange of 26% to 36%, it is known that a sufficiently practical level isattained whether the readout magnetic field is upward or downward.

Similarly, in the magneto-optical disks 10 at various values of y in thecondition of x=31 of Gd_(x) (Fe_(100-y) Co_(y))_(100-x) of theintermediate layer 14, a readout magnetic field of 400 Oe was appliedupward (in the recording direction) and downward (in the prior art).FIG. 10 is a graph showing the results of measurement of maximum CNR andcrosstalk at this time, in which the ordinate indicates the CNR andcrosstalk, and the abscissa shows x%. As clear from FIG. 10, the CNR isslightly higher in the upward readout magnetic field than in thedownward direction. The crosstalk is also lower in the upward direction.For a practical magneto-optical disk, when y is in a range of 0 to 16%,it is known that a sufficiently practical level is attained whether thereadout magnetic field is upward or downward.

As known from these results, when reading out the information recordedby light modulation recording, when the composition Gd_(x) (Fe_(100-y)Co_(y))_(100-x) of the intermediate layer 14 satisfies the relation of26≦x≦36 and 0≦y≦16, whether the readout magnetic field is applied in therecording direction or erasing direction, double mask MSR readout isenabled, and when the readout magnetic field is applied in the recordingdirection, a readout characteristic excellent in CNR and crosstalk isachieved. Incidentally, in the case of y=0, the composition of theintermediate layer is Gd_(x) Fe_(100-x).

Embodiment 3

Embodiment 2 refers to the readout characteristic of the magneto-opticaldisks 10 by light modulation recording, and in embodiment 3, by magneticfield modulation recording in magneto-optical disks 10, the CNR andcrosstalk were similarly measured. The magneto-optical disk 10 wasirradiated with a recording laser beam of 11.0 mW, and a recordingmagnetic field of 300 Oe was applied, and laser pulse magnetic fieldmodulation recording was effected. When recording, a magnetic field wasapplied from a floating head, and the recording frequency was 3.75 MHz.The laser beam was emitted by laser pulse (frequency 7.51 MHz) withpulse width of 40 ns, and same as in the case of light modulationrecording, record marks of 0.333 μm were formed. Prior to recording,meanwhile, to define the direction of magnetic field, an erasing laserof 8 mW was emitted, and a downward erasing magnetic field was appliedby 300 Oe, and the entire disk was erased.

In the magneto-optical disks 10 at various values of x in the conditionof y=6 of Gd_(x) (Fe_(100-y) Co_(y))_(100-x) of the intermediate layer14, and in the magneto-optical disks 10 at various values of y in thecondition of x=31, downward (in the erasing direction) and upward (inthe reverse direction of the erasing direction) readout magnetic fieldswere applied at 450 Oe from the floating head. FIG. 11 and FIG. 12 aregraphs showing results of CNR and crosstalk in both cases, in which theordinate indicates the CNR and crosstalk, and the abscissa shows x%. Asclear from FIG. 11 and FIG. 12, as compared with light modulationrecording (refer to embodiment 2), the CNR was higher and also a highervalue of crosstalk was obtained. This is considered because, in magneticfield modulation recording, larger record marks in the track widthdirection are formed than in light modulation recording.

As clear from FIG. 11, moreover, as far as x is in a range of 26 to 38%,whether the readout magnetic field is upward or downward, a readoutcharacteristic of practical level is obtained, and as also obvious fromFIG. 12, when y is in a range of 0 to 17%, whether the readout magneticfield is upward or downward, a readout characteristic of practical levelis obtained. Therefore, when reading out the information recorded bymagnetic field modulation recording, when the composition Gd_(x)(Fe_(100-y) Co_(y))_(100-x) of the intermediate layer 14 satisfies therelation of 26≦x≦38 and 0≦y≦17, whether the readout magnetic field isapplied in the erasing direction or its reverse direction, double maskMSR readout is enabled, and when the readout magnetic field is appliedin the reverse direction of the erasing direction, a readoutcharacteristic excellent in CNR and crosstalk is obtained.

Embodiment 4

The magneto-optical disks 10 same as in embodiment 1 in the compositionof the intermediate layer 14 of Gd₃₁.0 (Fe₉₄.0 Co₆.0)₆₉.0 werefabricated by various film thicknesses of the intermediate layer 14, andupward (in the recording direction) readout magnetic fields of variousmagnitude were applied, and the readout magnetic field was determinedwhen the readout crosstalk of each magneto-optical disk 10 became -40dB. As known from FIG. 13, as the film thickness increases, thecrosstalk of -40 dB is obtained by a smaller readout magnetic field, andwhen the film thickness is about 50 nm or more, the readout magneticfield is no longer decreased. A larger readout magnetic field is neededwhen the film thickness of the intermediate layer 14 is smaller, whichis because the exchange coupled force between the recording layer 14 andthe recording layer 15 becomes higher when the film thickness of theintermediate layer 14 becomes thinner, and therefore the magnetizationof the intermediate layer 14 is hardly aligned in the readout field inthe low-temperature region when reading out.

The practical level of the readout magnetic field is 500 Oe or less.Hence, the film thickness of the intermediate layer 14 is preferred tobe 15 nm or more. Incidentally, due to the practical limit of thicknessas magneto-optical disk, the maximum film thickness of the intermediatelayer 14 is about 60 nm.

Thus, in the invention, by specifying the composition of the secondmagnetic field, whether the readout magnetic field is applied in theerasing direction or in the reverse recording direction, double mask MSRreadout is enabled, and in the case of MSR readout by applying a readoutmagnetic field in the recording direction, a further higher resolutionis obtained, and the crosstalk is decreased, so that narrower tracks maybe realized, and many other excellent effects are brought about by theinvention.

As the invention may be embodied in several forms without departing fromthe spirit of essential characteristics thereof, the present embodimentsare therefore illustrative and not restrictive, since the scope of theinvention is defined by the appended claims rather than by thedescription preceding them, and all changes that fall within metes andbounds of the claims, or equivalence of such metes and bounds thereofare therefore intended to be embraced by the claims.

                  TABLE 1                                                         ______________________________________                                                                         CURIE                                                                         TEM-                                                                          PERA-                                        COMPOSITION       DOMINANT       TURE                                         ______________________________________                                        READOUT Gd.sub.25.0 (Fe.sub.83.0 Co.sub.17.0).sub.75.0                                              TRANSITION-METAL                                                                             280° C.                           LAYER                 MAGNETIZATION                                                                 DOMINANT                                                INTER-  Gd.sub.31.0 (Fe.sub.94.0 Co.sub.6.0).sub.69.0                                               RARE-EARTH     250° C.                           MEDIATE               MAGNETIZATION                                           LAYER                 DOMINANT                                                RECORD- Tb.sub.25.0 (Fe.sub.68.0 Co.sub.32.0).sub.75.0                                              TRANSITION-METAL                                                                             310° C.                           ING                   MAGNETIZATION                                           LAYER                 DOMINANT                                                ______________________________________                                    

We claim:
 1. A magneto-optical recording medium, comprising:a firstmagnetic layer formed from GdFeCo and having an easy direction ofmagnetization orthogonal to the plane of said first magnetic layer; asecond magnetic layer formed from GdFeCo, being rare-earth magnetizationdominant, laminated on said first magnetic layer and having, at roomtemperature, an easy direction of magnetization in the plane of saidsecond magnetic layer, said second magnetic layer comprising at leastGd_(x) (Fe_(100-y) Co_(y))_(100-y) of which x and y respectively satisfy26≦x≦38, 0≦y≦17; and a third magnetic layer laminated on said secondmagnetic layer and having an easy direction of magnetization orthogonalto the plane of said third magnetic layer.
 2. The magneto-opticalrecording medium according to claim 1, wherein said second magneticlayer has a film thickness ≧15 nm.
 3. A method for reading amagneto-optical recording medium having a first magnetic layer formedfrom GdFeCo and having an easy direction of magnetization orthogonal tothe plane of the first magnetic layer; a second magnetic layer formedfrom GdFeCo, being rare-earth magnetization dominant, laminated on thefirst magnetic layer and having, at a room temperature, an easydirection of magnetization in the plane of the second magnetic layer,the second magnetic layer comprising at least Gd_(x) (Fe_(100-y)Co_(y))_(100-x), of which x and y respectively satisfy 26≦x≦38, 0≦y≦17;and a third magnetic layer laminated on the second magnetic layer andhaving an easy direction of magnetization orthogonal to the plane of thethird magnetic layer; wherein information is recorded on themagneto-optical recording medium by forming a first region in the thirdmagnetic layer whose magnetization direction is inverted from a firstdirection to a second direction, and forming a second region whosemagnetization direction is maintained in the first direction, whereinthe recording of information is effected by irradiating a portion of themagneto-optical recording medium with a modulated intensity light beam,said method comprising the steps of:irradiating a magneto-opticalrecording medium with a light beam accompanied by a relative move; andreading out information by applying a magnetic field in said seconddirection at least in the region irradiated with the light beam.
 4. Amethod for reading a magneto-optical recording medium including a firstmagnetic layer formed from GdFeCo and having an easy direction ofmagnetization in the plane formed by the first magnetic layer; a secondmagnetic layer formed from GdFeCo, being rare-earth magnetizationdominant, laminated on the first magnetic layer and having, at a roomtemperature, an easy direction of magnetization in the plane formed bythe second magnetic layer, the second magnetic layer comprising at leastGd_(x) (Fe_(100-y) Co_(y))_(100-x) of which x and y respectively satisfy26≦x≦38, 0≦y≦17; and a third magnetic layer laminated on the secondmagnetic layer and having an easy direction of magnetization orthogonalto the plane formed by the third magnetic layer; wherein themagnetization direction of the third magnetic layer is aligned in afirst predetermined direction, wherein information is recorded on themagneto-optical recording medium by forming a first region in the thirdmagnetic layer whose magnetization direction is inverted from the firstdirection to a second direction, and forming a second region whosemagnetization direction is maintained in the first direction, andwherein the recording of information is effected by applying a magneticfield whose direction of magnetization is modulated, said methodcomprising the steps of:irradiating a magneto-optical recording mediumwith a light beam accompanied by a relative move; and reading outinformation by applying a magnetic field in said second direction atleast in the region irradiated with the light beam.